1. Field of the Invention
The present invention relates to plants and plant parts exhibiting inhibited or delayed fruit ripening or tissue senescence. In particular, the invention relates to edible Brassica plants which display a delayed senescence, at least at room temperature.
2. Description of the Related Art
A problem faced by growers of plants destined for consumption is that harvesting of plants of a marketable age generally has to be performed over a time course of from about one to four weeks. If the time course for harvesting is too long, the edible portions of plants start visibly to deteriorate on the plant and become of limited commercial interest to the grower and/or retail outlet supplier. Retail outlets such as super-markets and the like try to extend the shelf life of plant parts by utilizing measures such as cooled shelving, water sprays, the use of plastic foil wrappings and gas manipulation. Although these work to a degree, there is still wastage of plant material, and hence loss of sales. Edible portions include those portions which are typically sold in the fresh produce shelves of super markets and the like or are sold to the canning and/or pickling industries.
In climacteric plants, including many members of the Brassica family, there is a rise in the rate of respiration and an associated production of ethylene at the onset of fruit ripening and the senescence of green tissues. In non-climacteric plants these changes are not observed. Ethylene is believed to trigger the ripening of fruits and senescence in leaves of climacteric plants and it has previously been shown that the exogenous addition of ethylene to such plants promotes these responses.
Cytokinins have a pronounced effect on the delay of senescence in fruits and other plant parts of climacteric plants. Cytokinins also play a role in cell division, the formation of lateral shoots, sprouts, flowers and fruits. Cytokinins are believed to be actively involved in the senescence process of plants when in the active free base and riboside configurations. Conversion of the active configuration of cytokinin into an inactive configuration in Brassica plants involves the addition of a sugar or amino acid moiety to the N.sup.7.9 -of the adenine ring of the cytokinin.